1. Field of the Invention
The present invention relates to a zoom lens system, an imaging device and a camera. In particular, the present invention relates to: a high-performance zoom lens system that has a reduced size with a short overall length of lens system and still has a high resolution and a relatively high zooming ratio of 4 or greater and that is satisfactorily applicable in wide-angle image taking; an imaging device employing this zoom lens system; and a thin and compact camera employing this imaging device.
Further, in particular, the present invention relates to: a high-performance zoom lens system that has a remarkably reduced size with a short overall length of lens system and still achieves a high resolution and a zooming ratio of approximately 3 or greater and that is satisfactorily applicable in wide-angle image taking; an imaging device employing this zoom lens system; and a thin and compact camera employing this imaging device.
Further, in particular, the present invention relates to: a high-performance zoom lens system that has a remarkably reduced size with a short overall length of lens system and still achieves a high resolution and a zooming ratio of approximately 3 or greater and that is satisfactorily applicable in wide-angle image taking and further provided with a blur compensation function of optically compensating image blur caused by hand blurring, vibration and the like; an imaging device employing this zoom lens system; and a thin and compact camera employing this imaging device.
2. Description of the Background Art
Remarkably strong requirements of size reduction and performance improvement are present in digital still cameras and digital video cameras (simply referred to as digital cameras, hereinafter) provided with an image sensor for performing photoelectric conversion. In particular, in recent years, thin digital cameras are requested in which top priority is imparted to storability and portability. As one of means for realizing such thin digital cameras, various kinds of zoom lens systems have been proposed in which the light beam incident from the object is bent.
Japanese Laid-Open Patent Publication No. 2008-197594 discloses a zoom lens, in order from the object, comprising: a first lens unit fixed during zooming and having negative refractive power; a second lens unit fixed during zooming and composed of a prism for bending the optical path and not having refractive power; a third lens unit moved during zooming and having positive refractive power; a fourth lens unit moved during zooming and having negative refractive power; and a fifth lens unit fixed during zooming and having positive refractive power.
Japanese Laid-Open Patent Publication No. 2008-191306 discloses an image formation optical system comprising a positive lens unit, a negative lens unit and a diaphragm, wherein: the negative lens unit is arranged on the object side relative to the diaphragm; the negative lens unit has a cemented lens constructed by cementing a plurality of lenses; in at least one lens constituting the cemented lens, the physical properties of the glass material thereof are specified by two conditions; and a prism is provided for bending the optical path of the optical system.
Japanese Laid-Open Patent Publication No. 2007-279147 discloses a variable magnification optical system comprising a plurality of lens units for causing light from an object side to form an image onto an image surface of an image sensor, wherein the plurality of lens units, in order from the object side to the image side, at least includes a first lens unit having negative optical power, a second lens unit having positive optical power, a third lens unit having negative optical power, and a fourth lens unit having positive optical power, wherein the second lens unit moves within a plane perpendicular to the optical axis so that image blur on the image surface is compensated, and wherein the first lens unit includes an optical axis changing element.
Japanese Laid-Open Patent Publication No. 2007-108715 discloses an image formation optical system comprising a positive lens unit, a negative lens unit and a diaphragm, wherein: the negative lens unit is arranged on the image surface side relative to the diaphragm; the negative lens unit has a cemented lens constructed by cementing a plurality of lenses; in at least one lens constituting the cemented lens, the physical properties of the glass material thereof are specified by three conditions; and a prism is provided for bending the optical path of the optical system.
Nevertheless, in the zoom lenses and the optical systems disclosed in the patent documents, although size reduction is achieved to an extent applicable to thin and compact digital cameras, their zooming ratio is as low as approximately 3 or smaller and does not satisfy the requirement for digital cameras in recent years.
Further, the zoom lenses and the optical systems disclosed in the patent documents do not satisfy the requirements for digital cameras in recent years that the devices should be remarkably thin and compact and still applicable in wide-angle image taking.
Further, the zoom lenses and the optical systems disclosed in Japanese Laid-Open Patent Publication Nos. 2008-197594, 2008-191306 and 2007-108715 are not provided with a blur compensation function of optically compensating image blur caused by hand blurring, vibration and the like. Moreover, in the optical system disclosed in Japanese Laid-Open Patent Publication No. 2007-279147, although a blur compensation function is provided, a second lens unit located at a second position from the object side is moved in a direction perpendicular to the optical axis direction. Then, since the second lens unit is a lens unit to be moved during zooming, a mechanical configuration is required that realizes both of the movement in the optical axis direction and the movement in a direction perpendicular to the optical axis. This causes size increase in the lens barrel.